Heretofore, a thermoplastic polyester resin, mainly polyethylene terephthalate, has been widely used for various vessels and packing materials in the form of films or sheets because, in addition to excellent mechanical properties, the resin has gas barrier properties, transparency, chemical resistance, aroma-keeping properties, hygienic qualities and the like. Particularly, with the progress of blow molding technique, especially biaxial orientation blow molding technique, utilization thereof as hollow vessels such as bottles and cans has been remarkably developed.
However, vessels made of a thermoplastic polyester resin, mainly polyethylene terephthalate by biaxial orientation technique do not necessarily satisfy all requisite properties. Particularly, gas barrier properties thereof against oxygen are insufficient and these vessels are not suitable for packing food which requires high gas barrier properties.
As a resin having gas barrier properties, there has been known a saponified vinyl acetate copolymer. However, it is a crystalline resin and, when it is added to a thermoplastic polyester resin, orientation blow moldability is impaired. Further, the resulting hollow molded article shows pearl-like devitrification and does not have any substantial function as a transparent vessel. In addition, desired gas barrier properties thereof is hardly expected.
When a styrene-acrylonitrile copolymer is added, there is a drawback that the composition obtained can not be sufficiently oriented at an orientation temperature suitable for a polyester resin because of a high glass transition temperature (Tg) of the copolymer. Further, there is another drawback that the copolymer is a non-crystalline resin and orientation crystallization can not be introduced by orientation, which results in deformation of the resulting vessel due to an orientation release stress.
In the case of a simple blend of a thermoplastic resin and a polyamide resin having metaxylylene group, transparency of the resulting vessel is remarkably decreased and the use thereof is extremely limited.
The present inventors have intensively studied the oxygen barrier, mechanical, and transparency properties of thermoplastic polyester resins. Their study resulted in the discovery that adding a polyamide resin having a metaxylylene group and a compatibilizing agent to a thermoplastic polyester resin improves oxygen barrier properties without a deterioration of the mechanical and transparency properties.